Method for the emergency starting of an internal combustion engine in the case of a rotational speed sensor failure

ABSTRACT

The present invention relates to a method for starting a combustion engine that is equipped with a starter and a speed sensor which supplies an output signal as a function of the speed. Furthermore, a device for measuring the vehicle system voltage is provided which records the characteristic curve (3) of the battery voltage during starting phase (1) and after the starting phase (1). The crankshaft position is ascertained from the characteristic curve (3) of the battery voltage during the starting phase (1) of the combustion engine in starter operation.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for the emergency startof a combustion engine in the event of a failed speed sensor or speedsensors, in order to permit limited vehicle operation. If the speedsensor has failed, no allocation of a camshaft signal of a phase sensorto the crankshaft position is possible during the vehicle start.

BACKGROUND INFORMATION

[0002] The German Patent 40 26 232 relates to a device for monitoring aspeed sensor. The device includes a starter having a speed sensor thatsupplies an output signal as a function of the speed. A device formeasuring the vehicle system voltage is provided, and a control unit isprovided in which the output signal of the speed sensor is set inrelation to the vehicle system voltage, and a malfunction of the speedsensor is detectable. The characteristic curve of the vehicle systemvoltage is evaluated during the starting process of the combustionengine for the fault detection. A fault detection is only triggered whenthe characteristic curve of the vehicle system voltage typical for thestarting process is detected, and at the same time, no output signal ofthe speed sensor is detected.

[0003] If a speed sensor, which continuously samples a trigger wheel atthe crankshaft of a combustion engine, fails, vehicle operation underemergency conditions could also take place on the basis of theevaluation of the signals of a phase sensor. A speed signal, with whicha limited vehicle operation (limp home) is possible, is simulated fromthe phase sensor signal. If, on the other hand, the combustion engine isoperated with camshaft control, the location, i.e. the position of thecamshaft, and thus also the position of the crankshaft, is unknown inthe start, since the phase sensor is mounted at the indefinitelypositioned camshaft. Fluctuations may arise in the angular range up to40° arc of crankshaft rotation.

[0004] During the start of the vehicle, no allocation of the camshaftsignal and of the phase sensor to the crankshaft position is possible.Therefore, neither appropriate injection nor correspondingly matchedignition can be carried out by the further systems of the fuel injectionsystem. Consequently, a start of the combustion engine with camshaftcontrol is impossible if the speed sensor has failed.

SUMMARY OF THE INVENTION

[0005] Using the proposed invention, in the event of a failed speedsensor, the crankshaft position may be ascertained by evaluating thebattery voltage during starter operation.

[0006] Because of the actuation of the starter, which is supplied by avehicle battery, cyclically repeating compression and decompressionphases occur in the individual cylinders of the combustion engine to bestarted, be it a 4-cylinder or a 6-cylinder combustion engine. The endpoints of the compression and decompression phases, respectively, of theindividual cylinders of the combustion engine are determined essentiallyat the position of the bottom dead center (BDC) and the top dead center(TDC). According to the load of the starter during starter operationresulting from the compression and decompression phases of theindividual cylinders, the battery current of the energy accumulatorfeeding the starter assumes a characteristic curve from which thepositions of the respective TDC's and BDC's are determinable. If thestarter has finished a number of crankshaft revolutions, a reliableallocation of the individual TDC's and BDC's to the ascertained maximaand minima, respectively, of the battery voltage characteristic ispossible. If the allocation of maxima and minima to the respective TDC'sand BDC's is ensured, the injection and ignition at the correspondingcylinders of the combustion engine can be carried out via the enginemanagement according to the injection and ignition sequence stipulatedin the engine control electronics. The positions of TDC and BDC,respectively, ascertained from the maxima and minima of the batteryvoltage characteristic, can be stored by a corresponding correlationtable or a program map repeating the speed/load performance, and keptfor future purposes.

BRIEF DESCRIPTION OF THE DRAWING

[0007] The invention is explained more precisely below with reference tothe Drawing, in which:

[0008]FIG. 1 shows the characteristic curve of the battery voltage andof the engine speed during the operation of the starter and after thecombustion engine has started;

[0009]FIG. 2 shows the pulse signals of a 6-cylinder combustion engineduring the starting phase and after the start of the combustion engine.

EMBODIMENT VARIANTS

[0010]FIG. 1 shows the characteristic curve of the battery voltage andof the engine speed during the starting and after the engine hasstarted.

[0011] The diagram according to FIG. 1 shows characteristic curve 3 ofthe voltage of a motor-vehicle battery during starting phase 1 and afterthe start of the combustion engine. Starting phase 1, during which thestarter of a combustion engine cranks it via a few complete revolutionsof the crankshaft, takes place on first voltage level 9 made availableby the vehicle battery voltage source. Depending on the outsidetemperature, the internal resistance and the state of charge of themotor-vehicle battery, first voltage level 9 may lie considerably belowthat voltage level which is generated and maintained by the generator inthe combustion engine after the effected start of the combustion engine.Characteristic curve 3 of the voltage after the starting phase, whichasymptotically approaches a limiting value, shows second voltage level10 which is to be supplied by the generator of the combustion engine,and which should correspond essentially to the vehicle system voltage of12 volts. The second voltage level is independent of the state ofcharge, the outside temperature and the internal resistance,respectively, since it is supplied and maintained by the generator ofthe combustion engine.

[0012] Shown over time base 2, extending over a time span ofapproximately 4.5 s according to the exemplary embodiment in FIG. 1, isbattery-voltage characteristic curve 3 and the characteristic curve ofthe speed of the combustion engine. Graph 3 of the voltage duringstarting phase 1 shows that voltage 3 revolves in the shape of asinusoidal wave between minimally 4.1-4.n and maximally 5.1-5.n. Aspecific maximum 5.1, 5.2, 5.3 . . . 5.n coincides with a bottom deadcenter BDC 13, since there the load for the starter is the lowest.Maxima 5.1, 5.2, 5.3 . . . . . . . 5.n shown characterize the specifictop dead centers TDC's 12 of the 4 or more respective cylinders of acombustion engine to be started. The highest load acting on the starteroccurs shortly before reaching respective top dead center 12 of acylinder of the combustion engine, since all valves at the combustionchamber are closed, the elevated pressure prevails in the combustionchamber, the compression phase is terminated, and at this point, theinjection of fuel, and therefore, in the case of an Otto engine, theignition of the fuel/air mixture can take place. Injection and ignitionrepresent a further load of the battery voltage, which, however, is ofsecondary importance in the case here. Between individual maxima 5.1,5.2, 5.3 . . . 5.n and minima 4.1, 4.2 . . . 4.n, characteristic curve 3of the battery voltage has an edge 7 and an edge 8, respectively, risingand falling according to the compression and the decompression at thespecific cylinder, from which signals for the positioning of thecrankshaft may already be obtained.

[0013] To permit allocation of individual maxima 5.1 . . . 5.n andminima 4.1 . . . 4.n, respectively, between the individual cylinders ofthe combustion engine to be started, the starter must be actuated duringthe starting phase for a sufficiently long time phase. The allocationmust be implemented during the first combustion, since in response toerrors in the range of approximately 40° arc of crankshaft rotation,reversed rotation of the combustion engine or intake-manifold blowbacksmay occur, which, however, must absolutely be avoided.

[0014] The representation according to FIG. 2 shows the pulse signals ofa 6-cylinder combustion engine, both during starting phase 1 and inoperation, for example, during idling 10-.

[0015] Time base 2, extending over starting phase 1 and the firstrunning phase of the combustion engine, covers a time interval ofapproximately 4.5 s, analogous to time base 2 according to FIG. 1.During starting phase 1 of the 6-cylinder combustion engine, the pulsesat individual cylinders 1-6 take place in a first pulse duration 16,while according to FIG. 2, pulses 17 when a combustion engine has beenstarted are substantially shorter.

[0016] The correlation of top dead center 12 bottom dead center 13 withminima 4.1 . . . 4.n and maxima 5.1 . . . 5.n, respectively, yieldedfrom characteristic curve 3 of the battery voltage, takes place duringthe starting of the combustion engine and can be filed, for example, inan engine speed/load map and reused for later purposes, or may be storedin table form in the memory, e.g. in a ring buffer store of a controlelectronics for the combustion engine. Reference Numeral List:  1starting phase starter operation  2 time base  3 battery voltagecharacteristic curve 4.1-4.n minima 5.1-5.n maxima  6 turning point  7rising edge  8 falling edge  9 first voltage level 10 voltage levelsteady-state operation 11 first combustion 12 TDC 13 BDC 14 speedcharacteristic 15 ignition sequence 16 cylinders combustion engine 17pulse duration starter operation per cylinder 18 pulse duration normaloperation combustion engine

What is claimed is:
 1. A method for starting a combustion engine that is equipped with a starter a speed sensor which supplies an output signal as a function of the speed; and furthermore, a device for measuring the battery voltage is provided which records the characteristic curve (3) of the battery voltage during starting phase (1) and after the starting phase (1), wherein the crankshaft position is determined from the characteristic curve (3) of the battery voltage during the starting phase (1) of the combustion engine in starter operation.
 2. The method as recited in claim 1, wherein the maxima (5.1 to 5.n) and the minima (4.1 to 4.n) of the characteristic curve (3) of the battery voltage are ascertained during the starter operation (1).
 3. The method as recited in claim 1, wherein the position of top dead center (12) and of bottom dead center (13) of the cylinders of the combustion engine is determined from the characteristic curve (3) of the battery voltage.
 4. The method as recited in claim 1, wherein the starter of the combustion engine is actuated during the starting phase (1) of the combustion engine until a reliable allocation of the maxima (5.1 to 5.n) and minima (4.1 to 4.n) to the top dead center (12) and the bottom dead center (13), respectively, of the cylinders of the combustion engine is possible.
 5. The method as recited in claim 1, wherein the battery-voltage characteristic curve (3) during starter operation takes place on a first voltage level (9) dependent on the outside temperature.
 6. The method as recited in one or more of the preceding claims, wherein the correlation of the top dead center TDC (12) or bottom dead center BDC (13) of the cylinders of a combustion engine to the maxima (5.1 to 5.n) and minima (4.1 to 4.n), respectively, of the characteristic curve (3) of the battery voltage of the combustion engine is recorded in an engine speed/load map and stored.
 7. The method as recited in one or more of the preceding claims, wherein after the position of TDC (12) and BDC (13) of the cylinders of a combustion engine has been allocated to the ascertained maxima (5.1 to 5.n) and minima (4.1 to 4.n) of the characteristic curve (3) of the battery voltage, a first injection and ignition (11) take place.
 8. The method as recited in one or more of the preceding claims, wherein the characteristic curve of the battery voltage is used for the diagnosis or monitoring of the speed sensor or crankshaft sensor, and/or the phase sensor or camshaft sensor. 